Question
How in the world do you keep whitefly's off tomato plants

Answer
Adult and immature (nymph) stages suck fluids from plant foliage with their piercing-sucking mouthparts. Further injury may result from the sticky honeydew secreted by whiteflies, which adheres to foliage and fruits. This can result in a black sooty fungus (mold) growing on the honeydew that can interfere with leaf respiration.

Whiteflies can reduce yields of  tomatoes. To prevent yield loss, these insects must be controlled or kept to a low level during the growth period. Several insecticides are recommended for whitefly control on greenhouse grown tomatoes. These include dichlorvos (DDVP, Vapona) fog or mist; Thiodan WP, EC; malathion WP, EC; and naled (Dibrom EC, fog). Generally it is better to spray when temperature is 70o to 80o F. Spray applications every second day may be needed for 21 days in order to break their life cycle.

Combinations of the following insecticides could be applied if the incoming adult whitefly population is high: a pyrethroid with an organophosphate, carbamate or Thiodan; or soap with a pyrethroid or Thiodan. Apply based on the "Label" information. Do not apply Imidacloprid (Provado), Thiamethoxam (Actara) or products with similar chemistry if plants have been treated with Admire or Platinum. Highly UV-reflective mulches (metalized) and low rates of crop oil (0.25 -0.50 percent) could be used as whitefly repellents to reduce whitefly feeding and virus transmission.


Alternate insecticides if necessary.

A product called M-Pede Insecticide (contains potassium salts of fatty acids) produced by Mycogen Corporation is cleared for use on several greenhouse vegetables including tomatoes. Use of it will increase control of whiteflies. Use 1 part M-Pede per 100 parts of spray solution containing the companion pesticide. If small volumes of water are used, apply 1 ounce M-Pede per gallon of water. Overuse of M-Pede may cause phytotoxicity, especially when temperature is above 90o F.

Two of our major concerns in controlling whiteflies have been coverage and timing of our insecticide applications. Pyrellin EC (pyrethrin + Rotenone + cube resin) and Pyronone (pyrethrin + PB) may also be used alone or tank mixed with a companion insecticide. A product called Azatin EC (biological insecticide) may also be used on greenhouse tomatoes. This product produced by AgriDyne controls targeted immature (nymphs) whiteflies after they ingest or come in contact with it, by interfering with the insect's ability to molt. It is effective on all immature stages. This product can enhance your whitefly control if used properly. Use Azatin EC at least once per week when whiteflies appear, with an adulticide, and get complete coverage underneath and a top leaf surface.

Keep in mind whitefly eggs and pupae are generally not controlled with insecticides and only Azatin EC is effective on immatures. Correct timing and thorough coverage of insecticide is a must if whiteflies are to be kept under control. Read and observe all label usage and precaution statements.

Your local garden shop will also sell yellow sticky cards for measuring the number of adult whiteflies that are flying (this is what most commercial growers do). In a small garden setting, sticky cards may also manage your whitefly populations by killing the adults. Monitoring your populations, especially during hot dry weather will help you decide if or how to manage whitefly problems. Generally, tomatoes (and other plants) can tolerate some whiteflies (up to 10-25 nymphs per leaf) but population explosions (50 and up nymphs per leaf)